Screw

Library

First Generation/Joints

Description

Warning

This content is specific to Simscape™
Multibody™ First Generation software.
First-generation features are slated to be deprecated and should be avoided.

The Screw block represents a composite joint with one translational degrees of freedom (DoF) as
one prismatic primitive and one rotational DoF as one revolute primitive.
The translation and rotation axes are parallel. The translational
and rotational DoFs are constrained by a pitch constraint to have
proportional motion.

Satisfying Joint Requirements

A Joint block represents the relative degrees of freedom between
two bodies, not the bodies themselves.

You must connect any Joint block to two and only two Body blocks,
the base and the follower. All Joints have
two connector ports for these connections,
defining the direction of joint motion (base to follower). You connect
each side of the Joint block to these Body blocks at a Body coordinate system (CS) port.

You specify the joint primitive axes, if any, in the Joint dialog.

Assembly Restrictions on Assembled Joints

This Joint block is assembled and
places restrictions on the connected Body CSs.

If the Joint has no prismatic primitives, the origins
of the connected Body CSs on either side of the Joint must be spatially collocated points, to within assembly tolerances.

If the Joint has one or more prismatic primitives,
the origins of the connected Body CSs must lie in the span of the
prismatic axes:

Number of Prismatic Primitives

Span of Primitive Axes

One

Along the primitive axis

Two

In the plane of the primitive axes

Three

Anywhere in three-dimensional space

Dialog Box and Parameters

The dialog has two active areas, Connection
parameters and Parameters.

Connection Parameters

The base (B)-follower (F) Body sequence determines the sense
of positive motion. Positive rotation is the follower moving around
the rotational axis following the right-hand rule.

Current base

When you connect the base (B) connector port on the Screw block
to a Body CS Port on a Body, this parameter is automatically reset
to the name of this Body CS. See the following figure, Screw Base and Follower Body Connector Ports.

The base Body is automatically connected to the joint primitive R1 in
the primitive list in Parameters.

Current follower

When you connect the follower (F) connector port on the Screw
block to a Body CS Port on a Body, this parameter is automatically
reset to the name of this Body CS. See the following figure, Screw Base and Follower Body Connector Ports.

The follower Body is automatically connected to the joint primitive R1 in
the primitive list in Parameters.

Number of sensor/actuator ports

Using this spinner menu, you can set the number of extra connector
ports needed for connecting Joint Actuator and Joint Sensor blocks
to this Joint. The default is 0.

The motion of revolute primitives is specified in angular units.

Screw Base and Follower Body Connector Ports

Parameters

Switch between the Axes and Advanced tabs.

Axes Tab

The entries on the Axes tab
are required. Each DoF primitive in Screw has an entry line. These
lines specify the direction of the axes of action of the DoFs that
the Screw represents.

Name - Primitive

The primitive list states the name and type of the joint primitive
that makes up the Screw block: revolute primitive R1.

Axis of Action [x y z]

Enter here as a three-component vector the directional axes
defining the allowed motions of this primitive and its corresponding
DoF:

Revolute: axis of rotation

The default vectors are shown in the dialog above. The axis
is a directed vector whose overall sign matters.

Reference CS

Using the pull-down menu, choose the coordinate system (World,
the base Body CS, or the follower Body CS) whose coordinate axes the
vector axis of action is oriented with respect to. This CS also determines
the absolute meaning of forces/torques and motion along/about the
joint axis. The default is World.

The thread pitch controls the amount of translation for each
turn of the screw.

Thread pitch

Linear distance the screw travels along the screw axis for each
complete revolution of 2π radians (360o).
The default is 1.